Multi-objective optimization of the melting performance indicators of an eccentric horizontal shell and tube latent heat thermal energy storage system

In this paper, the concurrent effects of multiple enhancement approaches, namely, the adoption of downward eccentricity, increasing the fluid charging temperature, and the incorporation of graphene nanofiller (up to 3 vol%) to the phase change materials (PCM), on the melting performance of a double-tube energy storage system, are numerically explored. Three downward eccentric designs (with eccentricities of 0.2, 0.4, and 0.6), and one concentric design are investigated with three PCMs, which have different phase change temperatures of 55, 60, and 65 °C. The melting performance is evaluated by exploring the combined impacts of eccentricity with the PCMs. This is followed by a multi-objective optimization study conducted on three eccentric positions (0.2–0.6), with three volumetric loadings (0–3 %) of graphene nanoplatelets at three charging temperatures (75–85 °C) on the best PCM. The enthalpy-porosity approach is employed to develop a transient, 3D computational model that characterizes the melting behaviors of all systems, and the response surface methodology is used for optimizing the design parameters. For the developed module, the optimal results feature a moderate eccentricity of 0.3095, a higher charging temperature of 85 °C, and a medium-high graphene loading of 2.2514 vol% when RT-55 is used as a PCM. The optimized melting time, maximum enhancement ratio, and thermal energy storage are 75.4168 min, 74.6494 %, and 292.491 kJ, respectively. Additionally, Pareto fronts are included to identify the trade-offs among three optimal objectives in performance.